Background: Obesity is associated with higher breast cancer recurrence and death, higher prevalence of comorbid conditions, and poorer health and quality of life (QoL). African-American (AA) women have the highest prevalence of obesity (58.6%) as well as the highest breast cancer death rate and shortest survival of any racial/ethnic group. They also have highest rates of obesity-related comorbidities, including diabetes, hypertension, and death from diabetes and heart disease. Weight management after cancer diagnosis and treatment in AA breast cancer survivors is crucial to reduce their comorbidities and disparities in outcomes and improve their QoL. Intensive multicomponent lifestyle interventions have shown success, but are limited due to its resource intensiveness and poor accessibility and adherence. Objective: The proposed study will be the first to prospectively evaluate a free commercial web-based weight loss program (SparkPeople) in AA breast cancer survivors. SparkPeople, which is congruent with social cognitive theory, features educational and motivational articles and videos, self-monitoring tracking tools, healthy recipes, incentives, and social support communities including discussion forums, teams, challenges, and expert blogs. Specific Aims: 1) Determine feasibility of using an online commercial weight loss program in AA breast cancer survivors. 2) Collect preliminary data on effect sizes of changes in outcomes and potential mediators associated with the use of the free online weight loss program (from baseline to 3 and 6 months). Methods: Randomized controlled trial to pilot test the intervention among 70 AA breast cancer survivors. Treatment group participants (N=35) receive 3 months of active treatment (training to use the SparkPeople website, a FitBit activity monitor, along with weekly motivational reminders to use website) and 3 months maintenance (SparkPeople and FitBit without reminders). After 6 months, control group (delayed intervention) participants (N=35) receive the SparkPeople treatment, while those in the original treatment group will be followed for an additional 6 months to assess continued adherence and sustainability. Outcomes: Feasibility: accrual, retention, adherence, and sustainability. Primary treatment outcomes: weight, BMI, waist circumference, % body fat, fat and lean mass. Secondary treatment outcomes: caloric intake, physical activity levels, cardiopulmonary fitness, cardiometabolic risk factors (blood pressure, lipids, glucose, Hb A1C), quality of life, and social cognitive theory constructs (social support, self- efficacy, outcome expectations, self-regulation) Impact: If effective, this program offers promise as a convenient, efficient, and easily disseminated weight loss program. By addressing obesity in AA breast cancer survivors, this innovative study may provide important tools to help reduce their comorbidities, improve their quality and length of survival, and decrease health disparities.